Weed problems and farmers' weed management strategies in rainfed paddy agroecosystems of Sathing-Phra, Southern Thailand

A study of the agrarian system of Sathing Phra area, started in 1982, has pointed out that weed problems faced by all types of farmers were one of the three main "bottlenecks" of rainfed rice based cropping systems. Weed types and their degree of infestation in rice fields depend on the characteristics of the agro-ecological units identified in the area. Among weeds identified, "wild rice" is the most dreaded by farmers. It's increasing infestation appears to be linked with the recent changes in the system of land use. Very few rice fields can be replanted by farmers since the impossibility of control of water level in paddies creates too high a manpower demand over a short du ration. The technique of dryseeded broadcasting allows farmers to plant all their fields. But in this case weed competition is a serious limiting factor of rice yields. The highly time consuming technique of hand weeding generally combined with thinning-replanting technique can only be performed during a short duration defined by agro-ecological constraints. Therefore, only part of the paddies can be completely hand weeded. Added to ecological constraints, specific constraints of the three types of farming systems identified in the area have to be taken into account. Although numerous weed management strategies, especially wild rice ones, are employed, weeds cannot be properly control on all paddies. These observations provide basic information necessary for the launching of on-farm research on wild rice ecology and control in a cropping system perspective. (Résumé d'auteur